1. Field of the Invention
The present invention relates to a calibration method for a channel simulator, and more particularly, to a calibration method for a channel simulator, which is applied to a large-capacity channel simulator having the interfaces of P base stations and Q terminals so that path loss calibration for P×Q paths can be more rapidly and easily performed.
2. Description of the Related Art
Recently, as information society is accelerated, studies and researches have been actively carried out on multimedia communication systems to simultaneously process high-quality voice and data at high data rates. Meanwhile, mobile communication users have endlessly required higher-level communication quality, lower errors, and higher data rates, but designing a system required for a mobile communication channel is significantly difficult.
Under multi-path communication channels, line-of sight components, reflective components, and diffracted-wave components exist between a base station (BS), acting as a transmitter, and a mobile station (MS) or user equipment, serving as a receiver to exert influences on each other. The signals are received to a terminal and a Doppler spread occurs as the terminal is moved, which makes a propagation environment inferior to that of stationary communication.
In general, rural or suburban environments having the line-of sight signals may be explained using a Rician channel model, and composite signals caused by multi-paths, in which line-of sight components sparsely exist, represent Rayleigh distribution. In addition, the shading effect is appeared due to irregular surrounding topographies.
Since the wireless channels have significantly various propagation environments, the intrinsic performance of the wireless system must be represented even under different propagation environments. In order to ensure the performance of the wireless system, proto typing and a field test as well as the verification based on simulation and analysis are important to every service providers. However, the field test for a developed wireless system under all environments requires too much time, and costs. In order to more practically perform the field test, a real-time channel simulator must be used. The real-time channel simulator is referred to as a system capable of simulating almost all environments (The implementation of a multi-path fading channel simulator having a DSP-FPGA structure, volume 23, No. 1 (01, 2004), pp. 17-23, Joo-Hyun Lee et al).
Meanwhile, the fading mainly means the spatial variation of a signal intensity, but may mean the temporal variation according to the movement of a terminal. The fading includes a slow fading or long-term fading, such as propagation loss (path loss) in a free space, or the shadow effect, in which the intensity of a reception signal is slowly changed when the terminal is moved within a wide area, and fasting fading or short-term fading, such as frequency selective fading, frequency non-selective fading or Doppler spread fading, in which the intensity of the reception signal is rapidly changed when the terminal is moved in a narrow area. In a real environment, the slow fading and the fast fading are appeared together.
Until now, in order to realize a fading channel, an Okumura model, which is the most extensively used to estimate a signal in the downtown area, and a Hata model and a Jake model, which can be used even in a suburb and an open environment, have been employed. The slow fading is realized by simply applying only different delays for a starting signal according to various paths while the fast fading is realized by additionally multiplying the slow fading by a complex gain. Finally, the combination of the slow fading and the fast fading is output to the terminal or the base station.
Meanwhile, conventionally, a plurality of single channel simulators used to simulate an environment must be used between one base station and on terminal in order to simulate a real channel environment that a plurality of base stations and a plurality of terminals coexist to mutually affect each other, which significantly increases costs resulting from the repetition of the simulators in terms of functions or degrading the efficiency of space use. In order to solve the above problem, the applicant of the present invention has issued Korea Patent Registration No. 1286023 after filing the patent application on a large-capacity channel simulator configured to easily employ bi-directional path loss and bi-directional real-time fading.
In addition, when a large-capacity channel simulator is used, even if the same path loss (PL) is set to each of P base stations, Q terminals, and a channel simulator, when the base stations and the terminals are actually connected with the channel simulator, the PL may be varied due to various factors.
Therefore, in order to ensure the reliability of the analysis result through the channel simulator, it is very important to perform an advanced work that maintains all paths of the channel simulator with the same loss in the state that the base station and the terminal are actually connected with the channel simulator, and this work is referred to as calibration expressed as following Equation 1.
                                                                                          P                  ⁢                                                                          ⁢                  L                                =                                                      A                    ∘                    P                                    ⁢                                                                          ⁢                                      L                    ′                                                                                                                          =                                  (                                                                                                              P                          ⁢                                                                                                          ⁢                          L                                                                                            …                                                                                              P                          ⁢                                                                                                          ⁢                          L                                                                                                                                    …                                                                    …                                                                    …                                                                                                                                      P                          ⁢                                                                                                          ⁢                          L                                                                                            …                                                                                              P                          ⁢                                                                                                          ⁢                          L                                                                                                      )                                                                                                        =                                                      (                                                                                                                        a                            11                                                                                                    …                                                                                                      a                                                          1                              ⁢                              Q                                                                                                                                                                            …                                                                                                      a                            ij                                                                                                    …                                                                                                                                                  a                                                          P                              ⁢                                                                                                                          ⁢                              1                                                                                                                                …                                                                                                      a                            PQ                                                                                                                )                                    ∘                                      (                                                                                                                        P                            ⁢                                                                                                                  ⁢                                                          L                              11                                                                                                                                …                                                                                                      P                            ⁢                                                                                                                  ⁢                                                          L                                                              1                                ⁢                                Q                                                                                                                                                                                                          …                                                                                                      P                            ⁢                                                                                                                  ⁢                                                          L                              ij                                                                                                                                …                                                                                                                                                  P                            ⁢                                                                                                                  ⁢                                                          L                                                              P                                ⁢                                                                                                                                  ⁢                                1                                                                                                                                                              …                                                                                                      P                            ⁢                                                                                                                  ⁢                                                          L                              PQ                                                                                                                                            )                                                                                      ⁢                                  ⁢                              P            ⁢                                                  ⁢            L                    =                      (                                                                                P                    ⁢                                                                                  ⁢                    L                                                                    …                                                                      P                    ⁢                                                                                  ⁢                    L                                                                                                …                                                                      P                    ⁢                                                                                  ⁢                    L                                                                    …                                                                                                  P                    ⁢                                                                                  ⁢                    L                                                                    …                                                                      P                    ⁢                                                                                  ⁢                    L                                                                        )                          ⁢                                  ⁢                              P            ⁢                                                  ⁢                          L              ′                                =                      (                                                                                P                    ⁢                                                                                  ⁢                                          L                      11                                                                                        …                                                                      P                    ⁢                                                                                  ⁢                                          L                                              1                        ⁢                        Q                                                                                                                                          …                                                                      P                    ⁢                                                                                  ⁢                                          L                      ij                                                                                        …                                                                                                  P                    ⁢                                                                                  ⁢                                          L                                              P                        ⁢                                                                                                  ⁢                        1                                                                                                              …                                                                      P                    ⁢                                                                                  ⁢                                          L                      PQ                                                                                            )                          ⁢                                  ⁢                  A          =                      (                                                                                a                    11                                                                    …                                                                      a                                          1                      ⁢                      Q                                                                                                                    …                                                                      a                    ij                                                                    …                                                                                                  a                                          P                      ⁢                                                                                          ⁢                      1                                                                                        …                                                                      a                    PQ                                                                        )                          ⁢                                  ⁢                                            (                              A                ∘                B                            )                        ij                    =                                    a              ij                        =                                          b                ij                            :                              Matrix                ⁢                                                                  ⁢                Hadamard                ⁢                                                                  ⁢                product                                                                        Equation        ⁢                                  ⁢        1            
In Equation 1, PL represents a preset path loss matrix, PL′ represents a path loss matrix, which is actually measured, and A represents a calibration matrix that equally maintains the loss of all paths. As shown in Equation 1, when the PL calibration is performed with respect to a channel simulator connected with P base stations and Q terminals, since calibration works must be performed by the number of paths corresponding to the product P×Q of P and Q must be performed, efforts and time are significantly required only for the calibration.
In addition, since the PL calibration must be performed in the state that the base stations and the terminals are actually connected with the channel simulator, if the connections between the channel simulator and the base station or the channel simulator and the terminal are released or the PL is not exactly measured on a cable to connect the calibration simulator and the base station or the terminal during the calibration work, errors may occur.
As related art, there is Korean Patent Registration No. 10-1286023 entitled “channel simulator”.